This invention relates in general to a continuous catalytic reaction process utilizing a simulated moving catalyst bed to effect simultaneously in different zones of a catalyst bed containing at least three zones, a reaction of reactants and a reactivation of a catalyst in the catalyst bed, and more specifically, this invention relates to an application of a simulated moving catalyst bed to an alkylation reaction process.
One of the problems in carrying out a catalytic reaction is that of catalyst deactivation. In essentially all catalytic reactions, over a period of time the catalyst will lose part of its activity. It is common practice to discard or regenerate a catalyst when its activity is sufficiently low to cause inefficiency or unprofitability, at which point the catalyst is considered "spent". Various schemes are used to reactivate or regenerate a catalyst depending on catalyst characteristics, the process scheme and economic considerations. Generally, the operation to regenerate a catalyst is considered unprofitable, although at least in certain processes, some, and even a great benefit is directly derived from a catalyst regeneration operation. When an operating plant must be taken out of operation for the purpose of conducting a regeneration of a catalyst, and production time is lost, the economic liability is especially great. Typical examples of processes which require shutdown of normal operations to regenerate catalyst include naphtha reforming to high octane gasoline, hydrocracking, hydrodesulfurization, and di-olefin saturation, to name but a few, and in these processes, it is common for a plant to be shutdown about 2 to 10 percent of a calendar year for the purpose of catalyst regeneration. In other processes, the catalyst deactivation rate is so great that reactors must be installed in duplicate to allow normal operation in one, while regeneration or replacement of the catalyst in the stand-by reactor takes place. An example of such a process is a process for dehydrogenation of paraffins to olefins, but the technique of providing stand-by reactors or contactors is more common for simple operations like air drying. Another regeneration scheme is the recent development of continuous regeneration of a small portion of a catalyst bed by continuously removing a catalyst portion from the bed, regenerating it in continuous facilities external to the catalyst bed, and continuously returning regenerated catalyst to the catalyst bed. This method of catalyst regeneration has been successfully applied to a reforming process in which naphtha is upgraded to high octane gasoline. Still another regeneration technique is that commonly employed in fluid catalytic cracking units, wherein the entire catalyst bed is continuously moving between a reaction zone and a regeneration zone during normal operation.
Each of the above described regeneration schemes has benefits and liabilities which make the scheme applicable to a given process and not another. The continuous schemes are becoming more desirable as processing severity increases, resulting in more rapid catalyst deactivation. From a historical viewpoint, it is seen that economics favor increasing reaction severity for many catalytic reactions, resulting in higher product yields and higher product quality and a greater catalyst deactivation rate. While catalyst development has resulted in more active, more stable catalysts, emphasis is being placed on maintaining essentially fresh catalyst activity throughout the duration of a catalyst run. In many processes, the increased value of a higher product yield or higher product quality throughout a catalyst run is greater than the increased cost of maintaining a higher catalyst activity, either through more expensive, more stable catalysts or through continuous regeneration schemes.
While a new reaction/regeneration scheme may be applicable to many present processes, such a new scheme may also be applied to certain catalyst preparations which cannot now be economically utilized due to a combination of high catalyst deactivation rate and an unsatisfactory regeneration scheme.